1. Field of the Invention
The present invention relates to photographic film units including a disk of sheet film carried on a centrally located hub, and to methods of assembling such units. More specifically, the invention relates to structure and methods for accurately aligning a film disk on a central hub.
2. Brief Description of the Prior Art
U.S. Patent Application Ser. No. 774,716, entitled PHOTOGRAPHIC FILM UNIT AND CARTRIDGE ASSEMBLY, filed in the name of Donald M. Harvey on Mar. 7, 1977, discloses a miniature film unit that includes a disk of photosensitive sheet film supported on a hub. The hub is received through a central aperture in the film disk and is permanently attached thereto by a protruding hub finger, heat deformed onto the surface of the film. Alignment between the hub and film is predetermined by their respective dimensions, including their relative diameters, and by a key on the disk which fits closely in a hub keyway.
A more recent film-disk embodiment is depicted in U.S. Patent Application Ser. No. 931,053, entitled PHOTOGRAPHIC FILM CARTRIDGE ASSEMBLY AND CAMERA, filed in the name of Gurdip S. Sethi on even date herewith. In the Sethi embodiment, the disk is secured to the hub by trapping the disk between a hub flange and a retaining ring. Again, alignment between the hub and the disk is established by their respective dimensions.
Although the above-mentioned film disks offer many advantageous features, important advantages of the present invention are not available from the teaching of the prior art. By way of example only, the film units described above rely on the dimensions of the respective film unit parts to predetermine their assembled alignment. This causes a chain of undesirable tolerance requirements, from matched production lines, that must produce nearly identical parts, to final assembly equipment, that must rapidly mount one tight fitting part onto another. Additionally, there is a tendency for foreign matter to collect at the interfaces between the parts. During processing, for example, solutions from one processing bath may be transferred to and contaminate subsequent processing baths. Similarly, when the film unit is dried by spinning, a particularly desirable method, solution trapped at the interface may run across the film disk, causing streaks in the developed image.